USGS Science⌕ Search

Geology topics

T. J. Antrobus

Publications and source records attributed to T. J. Antrobus.

6 recordsLinked to original sources
USGS2007

Ordination of breeding birds in relation to environmental gradients in three southeastern United States floodplain forests

We used an ordination approach to identify factors important to the organization of breeding bird communities in three floodplains: Cache River, Arkansas (AR), Iatt Creek, Louisiana (LA), and the Coosawhatchie River, South Carolina (SC), USA. We used 5-min point counts to sample birds in each study area each spring from 1995 to 1998, and measured ground-surface elevations and a suite of other habitat variables to investigate bird distributions and community characteristics in relation to important environmental gradients. In both AR and SC, the average number of Neotropical migrant species detected was lowest in semipermanently flooded Nyssa aquatica Linnaeus habitats and greatest in the highest elevation floodplain zone. Melanerpes carolinus Linnaeus, Protonotaria citrea Boddaert, Quiscalus quiscula Linnaeus, and other species were more abundant in N. aquatica habitats, whereas Wilsonia citrina Boddaert, Oporornis formosus Wilson, Vireo griseus Boddaert, and others were more abundant in drier floodplain zones. In LA, there were no significant differences in community metrics or bird species abundances among forest types. Canonical correspondence analyses revealed that structural development of understory vegetation was the most important factor affecting bird distributions in all three study areas; however, potential causes of these structural gradients differed. In AR and SC, differences in habitat structure were related to the hydrologic gradient, as indexed by ground-surface elevation. In LA, structural variations were related mainly to the frequency of canopy gaps. Thus, bird communities in all three areas appeared to be organized primarily in response to repeated localized disturbance. Our results suggest that regular disturbance due to flooding plays an important role in structuring breeding bird communities in floodplains subject to prolonged inundation, whereas other agents of disturbance (e.g., canopy gaps) may be more important in headwater systems subject to only short-duration flooding. Management for avian community integrity in these systems should strive to maintain forest zonation and natural disturbance regimes. ?? 2007 Springer Science+Business Media B.V.

Wetlands Ecology and Management↗
USGS2005

Relationships between gap makers and gap fillers in an Arkansas floodplain forest

Question: In floodplain forests, does frequent flooding allow for self-replacement of shade-intolerant tree species or do small canopy gap openings lead to replacement by shade-tolerant tree species? Location: Cache River, Arkansas, US; 55 m a.s.l. Methods: The species, diameter-at-breast height, and elevation of primary gap-maker trees were determined for new gaps from 1995–1998. The size and species of gap-filler trees were identified and placed into three classes: definitive, edge, or interior. Transition probabilities were determined. Results: The dominant shade-intolerant species Quercus texana is being replaced primarily by the more shade-tolerant A. rubrum var. drummondii, Fraxinus spp. and Ulmus americana. Only 20 of 2767 gap fillers were Q. texana. Replacement probabilities are not constant across elevations, however, as the least shade-tolerant of the three most common species of definitive gap fillers, Fraxinus spp., occurred at lower elevations than A. rubrum var. drummondii , and U. americana. Conclusions: The contention that frequent flooding would allow for self-replacement of shade-intolerant species was only partially supported. The small canopy gaps undoubtedly influenced canopy replacement processes.

Arkansas↗
USGS2001

Canopy disturbance patterns in a bottomland hardwood forest in northeast Arkansas, USA

We characterized canopy disturbance patterns in a bottomland hardwood forest and identified linkages to tree species characteristics and interannual flooding patterns. We located 116 newly formed canopy gaps created by 136 gapmakers of 13 species. Over 83% of the gapmakers were snapped or uprooted (i.e., windthrow). The probability of any given gapmaker snapping or uprooting differed among years, species, and elevations. Neither wood properties nor diameter were major factors in determining the probability of snapping versus windthrow. Quercus texana , which had individuals with larger diameters-at-breast height than trees of other dominant species, was the most frequent gapmaker. The effects of elevation and flooding on the probability of snap versus windthrow seem to be tempered or amplified by interspecific rooting habits and tree morphology. Across species, windthrow occurred at lower elevations than snaps, and Q. texana and Q. lyrata showed differences in elevation between the two disturbance types. The total amount of area in newly-formed canopy gaps, as well as gap size, was relatively low compared to estimates for other forests. Our results suggest that natural disturbance patterns in bottomland hardwood forests are complex and are affected by the interactions among forest structure and composition and flooding patterns.

Arkansas↗
USGS2000

Vegetation dynamics

A disturbance can be defined as 'any relatively discrete event in time that disrupts ecosystem, community, or population structure and changes resources, substrate availability, or the physical environment' (Pickett and White 1985). Vegetation dynamics are a function of the temporal and spatial patterns of the disturbance regime. Natural disturbance regimes support the highest biological diversity; therefore, forest management practices that most closely mimic natural disturbances are expected to sustain the highest biological diversity within a given area (Denslow 1980). In southern forested wetlands, flooding is the dominant disturbance factor, thus plant species are usually distributed along a gowing-season flood gradient (Franz and Bassas 1977).

Book chapter↗
USGS2000

Bird community composition

Neotropical migrants are birds that breed in North America and winter primarily in Central and South America. Long-term population studies of birds in the Eastern United States indicated declines of some forest-dwelling birds, many of which winter in the Neotropics (Peterjohn and others 1995). These declines were attributed to loss of wintering and breeding habitat due to deforestation and fragmentation, respectively. Many species of Nearctic migrants--birds that breed in the northern regions of North America and winter in the Southern United States--are also experiencing population declines. Because large areas of undistrubed, older, bottomland hardwood forests oftern contain large numbers of habitat specialists, including forest-interior neotropical migrants and wintering Nearctic migrants, these forests may be critical in maintaining avian diversity. This study had two primary objectivs: (1) to create a baseline data set that can be used as a standard against which other bottomland hardwood forests can be compared, and (2) to establish long-term monitoring stations during both breeding and wintering seasons to discern population trends of avian species using bottomland hardwood forests.

Book chapter↗